1. Field of the Invention
The present invention relates to a method and apparatus for powering D.C. loads from a higher rated D.C. voltage supply.
2. Description of the Related Art
Many designs for delivering a lower D.C. voltage to a load from a higher D.C. voltage have been design in the past. One of these approaches includes the use of resistive elements, such as a rheostat or equivalent resistors in series. Obviously, this is a very inefficient way of stepping down a D.C. voltage since a substantial amount of energy would be dissipated as heat.
Other approaches involve the use of rather complicated circuitry, such as DC/AC converters and DC/DC converters. These are not only complex and expensive but also inefficient.
The present invention provides a novel approach to solving this problem by using a time interval modulation technique, as it will be explained below. Let""s use the example of a golf cart xe2x80x9celectric vehicle) with a 48 volts, D.C. electrical power source and, for simplicity""s sake, three accessories or loads that work with more common 12 volts D.C. inputs. Load No. 1 could be a horn; load No. 2 will be a halogen lamp and load No. 3 a fan. It has been found that these accessories do not require the application of the rated 12 volts at all times for them to function. Recognizing that 12 volts is 25% of 48 volts, it has been found that if the 48 volts supply voltage is applied with a 25% duty cycle, most of these accessories work. For example, the horn (load No. 1) works when the 48 volt supply is applied with a duty cycle of even 10%.
What is important is to realize that the different accessories, depending on their designs, will have different working ranges of duty cycles under a higher D.C. voltage than what they are rated.
Additionally, different periodic time slots of the 48-volt source can be allocated for each load or accessory. In this manner, there is an added advantage of avoiding loading down the source by operating two or more accessories simultaneously. This would eliminate the common xe2x80x9clight-dim-with-horn blowxe2x80x9d effect commonly experienced in these situations.
Of course, the high voltage supply, in this example the 48 volts, will be made available with a square waveform with a sufficient duty cycle to permit the allocation of contiguous time slots for each of the loads being serviced. The width of the time slots or pulses will vary with the requirements of each accessory or load.
Another benefit of this invention is that these periodic waveforms are susceptible to being measured through pick up coils in order to measure the amount of electricity used by the loads. This cannot be accomplished with purely DC driven accessories.
It is one of the main objects of the present invention to provide an apparatus and method that permits the use of a high voltage source to power lower voltage rated loads or accessories efficiently.
It is another object of this invention to provide such an apparatus and method that permits the powering of said loads independently from each other so there is no interference.
It is yet another object of this invention to provide such a device that is inexpensive to manufacture and maintain while retaining its effectiveness.
Further objects of the invention will be brought out in the following part of the specification, wherein detailed description is for the purpose of fully disclosing the invention without placing limitations thereon.